board: ti: am43: Fix DCDC3 voltage for epos-evm

A common voltage of 1.35V was being programmed for all am43 board
versions. EPOS-EVM Needs 1.20V for LPDDR2.

Fixes: fc69d472 (“board: ti: AM43XX: Add ddr voltage rail configuration”)
Reported-by: James Doublesin <doublesin@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>